Two marbles are released at the same height on two ramps that end at the same height. One has an decline then a flat surface. The other has a decline, a decline again, and then an incline. Which marble will get to the end first? How will their velocities compare? This lab for middle school aged kids is a great way to make observations on motion, forces, and stability.
One way to run this lab is to get the Arbor Scientific Racing Marbles Lab Kit. The kit comes with the marbles and the ramps. The teacher can chose to get the photogate with the kit to measure velocity, or they can use carbon paper. The attached lesson and lab worksheet describes how this lab can be done in class. The Arbor Scientific website also has videos explaining the concepts.
If funds are needed to get the ramps and photogate, consider applying for a classroom grant through the STEM Action Center.